3-Dihaloacetyl oxazolidine compounds prepared herein are known compounds; they are particularly useful as antidotal (safener) compounds to lessen or eliminate injury to crop plants by herbicidal compounds.
The 3-dihaloacetyl oxazolidine compounds discussed herein have been prepared by a variety of processes, all of which proceed through the corresponding non-haloacetylated precursor oxazolidine compound. The latter compounds have been prepared by the reaction of mono- and dihydric amino alcohols, e.g., ethanolamine or propanolamine, and an aldehyde, such as acetaldehyde, or a ketone, such as acetone. Such processes have been disclosed, e.g., by M. Senkus, J.A.C.S. 67 1515-1519 (1945) E. D. Bergmann, Chem. Rev. 53,309-352, especially 310-315, (1953) and by I. E. Saavedra, J. Org. Chem,. 1985, 50, 2379.
In adaptations of the above Senkus and Bergmann processes, K. D. Petrov et al. (Chem. Abs. 68 3840 (1967) describe the preparation of 3-(2-hydroxyethyl) oxazolidine by the reaction of furfurylaminoethanol or tetrahydrofurfurylaminoethanol and dihydroxyethylamine. Also described by Petrov et al are modifications involving the reaction of N-(2-hydroxyethyl) oxazolidine with the appropriate aldehyde, ketone or RCO.sub.2 Et ester containing sodium to prepare oxazolidine compounds substituted in the 3-position (i.e., the N atom), e.g., with such radicals as C.sub.3 H.sub.7 CO.sub.2 C.sub.2 H.sub.5 -, C.sub.6 H.sub.6 OCH.sub.2 -, etc.
The above process is also described in various patents which further show the reaction of the formed oxazolidine with a dihaloacetyl halide compound, typically dichloroacetyl chloride, to produce the corresponding 3-dichloroacetyl-(un)substituted oxazolidine compounds. Representative of such prior art patents include U.S. Pat. Nos. 4,038,284 and 4,278,799; EP Patent Applications 0 136 016, 0021759 and 190105 and GB Patent No. 1,544,679.
Another process for producing 3-dichloroacetyl (un)substituted oxazolidines includes the reaction of epichlorohydrin with the appropriate secondary amine (EP 0253 291).
Yet another process for preparing 3-dichloroacetyl oxazolidine which are characterized by having (un) substituted heterocyclic radicals in the 5-position is described in U.S. Pat. No. 5,225,570. The process described in this patent involves the reaction of a selected heterocyclic aldehyde, e.g., 3-furaldehyde, 2-thiophenecarboxaldehyde, etc., with cyanotrimethylsilane and zinc iodide to produce, e.g., 2-thiophenesilylcyanohydrin, which is reacted with lithium aluminum hydride to produce .alpha.-(aminoethyl)-2-thiophenemethanol. This material is then reacted with a ketone, e.g., acetone, methyl ethyl ketone, methyl phenyl ketone, etc., or an aldehyde, e.g., acetaldehyde,furaldehyde, tetrahydrofurfural, etc., to produce the corresponding oxazolidine, e.g., 2,2-dimethyl-5-(2-thienyloxazolidine), which is then reacted with a dihaloacetyl halide, e.g., dichloroacetyl chloride, to obtain the corresponding 5-(dichloroacetyl)-2,2-dimethyl-5-(2-thienyloxazolidine. A process modification disclosed in the U.S. Pat. No. 5,225,570 patent involves the reaction of an .alpha.-aminomethyl heterocyclicmethanol, e.g., .alpha.-aminomethyl furanemethanol, and an aldehyde, e.g., acetaldehyde, in an inert solvent, e.g., methylene chloride, and an acid acceptor, e.g., pyridine, to form the corresponding oxazolidine, which is then reacted with dichloroacetyl chloride to obtain the final product.
Since the process according to the present invention involves the catalytic hydrogenation of nitroalcohols, brief mention is made of prior work in this area of chemistry. It is well known that nitro groups can be reduced to amines in the presence of hydrogen and a metal catalyst; see, e.g., Rylander, "Catalytic Hydrogenation Over Platinum Metals" Academic Press, New York, 1967. It is further known that amines can be derivatized by treatment with aldehydes and ketones in the presence of hydrogen and a catalyst so that reductive alkylation takes place to give primary, secondary or tertiary amines; see Rylander, ibid, and March, "Advanced Organic Chemistry", Wiley Interscience, New York, 1985.
As a further extension of the above chemistry, it has been shown that reductive alkylation has been carried out on nitro compounds such that they are reduced in situ to primary or secondary amines; see March, ibid, and Emerson, "Organic Reactions, Vol. 4," John Wiley & Sons, New York, 1948. For example, a mixture of nitromethane and acetone with hydrogen and platinum gives methylisopropylamine (see Emerson et al, J. Am. Chem. Soc. 63,749 (1941). Similarly, an alkanolamine, such as ethanolamine, when reacted with acetone, hydrogen and platinum gives N-isopropyl ethanolamine; Cope and Hancock, J. Am. Chemo Soc., 64, 1503 (1942).
Aminoalcohols are difficult to prepare and isolate, because of undesirable by-product formation, such as N-alkylation, as well as promoting reverse reaction ("Retro-Aldol") of the starting nitroalcohol; (U.S. Pat. Nos. 2,347,621, 2,587,572 and 3,564,057).
Therefore, a need exists for a process which could eliminate the need to isolate aminoalcohols in catalytic hydrogenating processes.
Further, the ability to carry out the direct conversion of a nitroalcohol to an oxazolidine compound (useful as an intermediate in the preparation of antidotal 3-dichloroacetyl oxazolidine compounds) would be extremely beneficial due to: (1) the elimination of the need to isolate the intermediate aminoalcohol and oxazolidine starting materials; (2) improvement in reaction cycle times and (3) generally greater process efficiency.
Accordingly, it is an object of this invention to provide a novel process for the catalytic hydrogenation of nitroalcohols in the presence of aldehydes or ketones which avoids undesirable N-alkylation by-products and the need to isolate aminoalcohol, thus permitting in situ reduction and conversion thereof to the corresponding oxazolidine intermediate useful in the production of herbicidal antidote compounds. The achievement of this objective and concomitant advantages is completely new and unexpected.